Magnesia-containing refractories



Patented Nov. as, 1944 UNIT-ED STAT as PArsN'r oi-frlcs .iraclmsmbomsnmm amao'roams Rob'ert LaSchoeniaub, 'rlmn, om; mlto Refrac Basic :poration of Ohio tories,lnc., ,clev'eland, Ohio, a'oor No Drawing. Application my calm, a BCHIINO- 45am icclslms. (ct loo-sat Magnesia isextensively used in refractories in metallurgical hearths, furnace parts, etc.,' periclase refractories being made from magnesites, brucites, bitter-n or sea water precipitates, and similar materials. These materials arecalcined at high temperatures to render the product dense, impervious, chemically resistant and vollime-stable. The resulting granular productor clinker may be used :in this form for heanths, or may, be sized, bonded-"and formed into structural shapes. A major problem in the manufacture and use of periclase "refractories is-the control of substances associated with magnesia raw materials. The natural impurities in commercial magnesia materials, if properly managed, permitrefractories to be made at lower cost, and in suitable instances improve the product, such as by acting as bonding agents, preventing destructive absorption by encasement of the periolase grains,

and thebreaking of the continuity of the natural cleavageplanesof- .periclase, etc. Minor constituents commonly .foundin commercial periphysically somewhat less stable than forsterite- Both dicalcium silicate and forsterite clinkers are much more difficult to burn than an impervious and dense structure.

from raw materials containing quite large amounts of lime, but-they arf'chemically and clinkers.

comparable monticellite clinkers. A desirable commercial refractory would'be onein which the clinker could be easily and quickly coalesced to more. it would be so compounded in its ultimate form, as for instance brick, that itbecomesmore refractory than its component clinkers. A known clase refractories are orthosilicates, and the particular kind of orthosilicate is determined by the ratio of limeand silica present. Lime and mags nesia will combinewith silica to form dicalcium silicate (ZCaOSiOz), merwinite tories are, to a large extent, determined by the amount and kind of silicates present. Clinkers containing, 8 to 15 per cent silicate can give verysatisfactory results. Clinkers containing dicalcium silicate or forsterite are refractory and strong ati high temperatures, dicalcium silicate softening only at 3521' It, and forsteri'teat. 3398' F. ,Clinkers containing monticelllte are soft at high temperatures, monticellite softening at 2700' 1". In, some cases, such as inmetallurgical 'hearths,-monticellite in minor-amount may have utility. Periclase-fosterlte clinkersx areuu'ite stable pliysically and chemically. Howeventhey cannot made from-raw materials containing much lime. and even the smallamount of lime; which seems inevitably presentin the best rawmaterials softens them --to some extent. Peri- 3 plied effectively to monticellite-periclase clinker fabricated into bricks, or togranular hearth re-,.

Practice has been to blend monticellite olinkers with other clinker or materials containing excess (290, such that the materialsmutually correct each other to dicalcium silicate. Another method" has been to add to a periclase-monticellite clinker enough lime,calcium ferrite, or other lime compound to form dicalcium silicate and eliminate the monticellite. |A difficulty with these methods has been that they require chemical reaction of constituents which are ,well sealed in clinker.

grains, and thus involve a slow migration through a solid body, or first fusion and then reaction, but the fusion dest oys volume-stability.v The addition of calcium oxide or simple compound of calcium oxide also introduces diiliculties, because they are atmospherically unstable, evolve disruptive gases in the burning process, or intro;

duce materials deleterious to refractoriness. In

accordance with my present invention, monticellite in periclase refractorie may be corrected to dicalcium silicate in a novel manner not requiring the addition of unstable. expensive, disruptive,

or deleterious compounds of can. It canbe'apfractories, By the presentinvention, the monti-' cellite in even very coarse clinker grainscan' be corrected by additions to the fine matrixto obtain a desirable ingredient volume stability and strength at high temperatures. A'further particularly surprising" feature of the invention isthat it becomes possible to reduce'tlre silicon con-- tent and increase"calcium. The process a volumestabllity previously unobtainable in such compositions and to entirely'unexpected ex- .tent dries up such-materials when heated at tem- .peratures of about 3000" F. Other objects and appear-from the. following .de-'

advantages will scription.

To the accomplishment :-of the foregoing-and related ends, the invention, then comprises features hereinafter described. and-pmlcu- 1 1 pointed out in theolaims, the foiiow nl descripti n setting forth inseam comm illustrai f Flirthertive embodiments of the invention, these being indicative however, of but a few of the various ways in which the principle of the invention may be employed. v

In accordance with the invention, periclase refractoriescontaining monticellite, with or without dicalcium silicate. are subjected to the action of fluorspar. That this can result in an increase in the refractoriness is quite surprising, in that, fluorspar has commonly been known as a low melting flux, and it is customarily added to glass,slags and enamels to lower the melting temperatures and promote fusion. The combination however including periclase as here, involves quite different factors. With refractory compositions based on periclase, the present process is particularly desirable with magnesia clinkers containing more than 80 to 90 per cent magnesia,

and in general there is usually not much reason from a practical standpoint to operate the process in compositions below about, 70 per cent MgO.

And in general, up to about 10 per cent of fluorspar is applied. The amount required for correction in any given instance may be approximately determined by simple calculation. The ultimate composition that the refractory assumes without correction when fired-to furnace temperature is determined. 'Then the molecular equivalent of CaO is subtracted from the molecular equivalent of twice ,the silica. This difference multiplied by '18 is the weight of fluorspar required. Otherwise expressed, the correctionis as follows: 1

Let a:=per cent of Si=+6il (molecular equivalent of y=per cent of CaO+5 8 (molecular equivalent of C'aO) 4 Fluorspar required for correction= (2:12-11) '78.

As an example, a clinker of the following chem.- ical composition is to be made into a volume-stable brick:

Percent 810: 5.78 Ii'eaO: j 4.50 A120: 1.84 (7120: 2.20 CaO 6.95 M80 l 'luorspar required=(2-0.0940.124)78'=4.99 lbs. fluorspanper 100 lbs. of clinker. I

Often it may be desired-t0 underor over-correct. Inramming-mixtures,asanexample, some softness of clinker might be desirable. In

case's, the'm'onticellitemay he 70,.80 or- 90% corrected. In other cases, in which a brick may be exposed to siliceous sla'gs or silicadrop, it may be desirable to over-correct to .bui'f the silica pickup. The degree of correction most suitable for any given condition is best determined by empirical methods. The correction appearsnottobeatallcriticalandtobewell achieved by a simple correction as exemplified above.

Apparently, isolates the fluorspar and prevents its abrupt reaction with silicates over narrow temperature ranges. but .with higher temperatures the reactions proceeding to favorable results are consummated by diilusion and at temperatures of around 3000 F. are substantially complete, The systems so produced are devoid is of liquid, and no traces of fluorine compounds are visible microscopically. In fact, the fluorine appears to be. eliminateclby volatilization as the temperature exceeds 2800 F., and samples which is initially contain 6 per cent of fluorspar show less than a tenth of 1 per cent fluorine on analysis after heating to 3000 F. for-8 hours. A further pecularity is that oxides of silicon particularly, also iron and chromium to some extent, are rem moved. It will thus be readily seen that there is a fundamental distinction between the present process and the process of changing monticellite into dicalcium silicate by adding (78.0. The correction of monticellite with cs0 or its' Where dicalcium silicate is a component of the working composition, on account of its tendency to invert, it is desirable to incorporate in the clinker during the original burning, a small so amount of stabilizer, as known'for such piir-' pose, such as borates, phosphates, or chroma'tes.

For example borates in amount to give 0.06 per cent B: in the refractory obviate any diiiicuity. It is also desirable to add a small amount of staa bilizer, preferably 1320:, to the lines during the incorporation of fluorspar. If the'brick is burned prior to sale, the dicalcium silicate formed will be stabilized by such addition. If the brick is sold as an unburned chemically-bonded refrac- 40 tory, inversion is less of a problem, as the'predominant silicate at the inversion temperature will be unreacted monticellite.

- While, as indicated, the invention may be applied to all refractory compositions containing" as characteristic component, the foligwing specific examples will illustrate the inven- Brick: 30 per cent Guleman chrome are containing3per centof silica,anda siaed 5o clinker are compounded, the clinker having the 810: 4 per cent, l'eaOs 3percent,AlaO:1.percent,CaO4percent,MO 88percent,andBsps0.05percent. j

Chrome are 8 to 35 mesh... 30 Clinker 8 'to 35 mesh. 35 clinker 100 mesh... 3 5

Thisb'rlck composition may be chemically bondedwithlpartofcachfor example,driedina humidity drier, and sold wifliout'flring. Alter natively. it may be formed with 1 part of goulac orsulphiteliquorbindendriedandflredtomo' 1?. forihouraandbeused'asaburnedbrick.

Granular hearth materialiAhearthmaterlal wouldb'e.from'4meshclinkerof theBiOiS 1u-cent,Al:0 s2percent,Oa0'lpercent, 8 percent. 'Itwouldbe andfor'lilo partsof clinker 3.2 parts of meshilucrspar'wouidberolledontothetar. 'I'hiswould' beappliedwithcutslaggin'g percent, mo; 8 per modes of aplflrina principle ofithe invention may be employed, change being made as regards the details described, provided the fealeast 70 per cent, chromite, monticellite, dical-' cium silicate, and fluorspar in proportion up to per cent to correct at least a part of the monticellite to a more refractory silicate.

4. A refractory comprising magnesia clinker at least '10 p r cent, monticellite, dicalcium silicate, and fluorspar up to 10 per cent.

5. A refractory comprising magnesia, a magnesla-containing silicate, and material consisting of nuorspar in proportion to react with such silicate and form a more refractory silicate.

6. A refractory of magnesia clinker containing at least 70 per cent of magnesia, chromite, and monticellite and fluorspar to correct at least a part of the monticellite to a more refractory silicate.

7. A refractory of magnesia clinker containing at least 70 per cent of magnesia, and monticellite and fluorspar to correct at least a partof the monticellite to a more refractory silicate.

8. A refractory of magnesia clinker and a low melting silicate and material consisting of fluorspar in proportion to react with such low melting silicate and form a higher melting silicate.

9. A process of making refractories, which comprises mixing chromite and at least per cent magnesia, monticellite, and up to 10 per cent of fluorspar, forming into shapes, and firing.

10. A process of making refractories, which comprises mixing at least 70 per cent magnesia,

monticellite, and up to 10 per cent of iiuorspar,

forming into shapes, and firing.

11. A process oi, making refractories, which comprises mixing at least 70 per cent magnesia. and monticellite, and up to 10 per cent of fluorspar.

12. A process of making refractories, which comprises removing silicon from a magnesiamonticellite refractory composition by adding fluorspar and firing. a

13. A process of making refractories, which comprises obviating effects of silica absorbed from. furnace drip, slag, vapors, etc., by adding material consisting of fluorspar to a magnesia refractorycontaining low melting silicate in proportion to react with such low melting silicate and. form a higher melting silicate.

14. A process of makingjrefractories, which comprises mixing ground burned magnesia and monticellite, and fluorspar in proportion to correct at least a part of the monticellite to a more I refractory silicate.

15. A process of making refractories,- which comprises reducing shrinkage in service tempera-' ture in a refractory of materials containing magnesia and monticellite by adding up.to1 10 per cent of fluorspar before firing.

16. A process of making refractories, which comprises converting monticellite in a periclase refractory to a more refractory silicate by adding fluorspar and firing.

ROBERT A. SCHOENLAUB. 

